Colin Firth has joined the cast of the upcoming true crime drama Devil's Knot.

The film, based on journalist Mara Leveritt's 2002 book Devil's Knot: The True Story of the West Memphis Three, will tell the story of the 1993 murders of three children and the subsequent arrest, trial and sentencing of three teenagers for the crime.

The convicted defendants were released from prison last year due to a lack of evidence.

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According to The Hollywood Reporter, Firth will star alongside Reese Witherspoon, who has signed on to play the mother of one of the murdered boys.

It is not currently clear what role Firth will take on in the upcoming drama, which is being shopped to international buyers at this year's Cannes Film Festival by The Weinstein Company.